PLATE IV. 



Page. 

 SPIRIFERA PI^ONENSIS 138 



Figs. 1, 1 a, I. The original figures of S. argentarius Meek. 

 1 c, e,f. The original figures of S. Pinonensis Meek. 



1 d. Dorsal view of a specimen from the Eureka District, in which the radiating pli- 

 cations are finer than in fig. 1 e. Natural size. 



SPIRIFERA RARICOSTA 135 



Fig. 2. Ventral valve of a specimen with numerous plications. 



2 a. Same view of a shell with few plications. See plate xiv, fig. 12. 



TREMATOSPIRA INFREQUENS 151 



Figs. 3, 3 a, b. Dorsal, ventral, and side views of the type specimen. Natural size. 



CRYPTONELLA PI^OXENSIS 163 



Fig. 4, 4 a, b. Dorsal, ventral, and side views of the type specimen. Natural size. 



MYTILARCA DUBIA 168 



Fig. 5. Cast of right valve. Natural size. 

 5 a. View of anterior side. 



POSIDONOMYA L2EV1S 178 



Fig. 6. Eight valve. Natural size. 



POSIDONOMYA DE VONICA 179 



Fig. 7. Right valve enlarged to two diameters. 



MODIOMORPHA OBTUSA 171 



Fig. 8. Cardinal view of right valve. 

 8 a. Right valve. Natural size. 



MYTILARCA CIIEMUNGENSIS 168 



Fig. 9. Right valve. Natural size. 



SANGUINOLITES ? GRACILIS 175 



Fig. 10. Right valve. Natural size. 



